Despite an efficient combination antiretroviral therapy (cART), the persistence of HIV-1 reservoirs, harboring transcriptionally silent but replication-competent stably integrated HIV-1 proviruses, seriously challenges the hope of HIV-1 eradication from cART-treated HIV-infected individuals. Indeed, the HIV-1 reservoirs are insensitive to cART and able to escape from the host immune response. Therefore, these latent reservoirs are a permanent source for virus reactivation and could be responsible for the rebound of plasma viral load observed after cART interruption. Consequently, cART treatment requires lifelong adherence, leading to several long term side effects and a life expectancy lower than that of uninfected individuals. Several therapeutic approaches aiming at achieving either a sterilizing cure (elimination of HIV from the human body) or—more likely—a functional cure (long-term control of HIV infection and disease progression in the absence of cART) have been proposed. In this context, reactivation of HIV-1 gene expression in latently-infected cells together with an efficient cART could serve as an adjuvant therapy aimed at decreasing the pool of persistent reservoirs.
HIV-1 transcriptional inhibition is crucial to the establishment and maintenance of post-integration latency. The chromatin organization and the epigenetic control of the HIV-1 promoter are key elements in this transcriptional silencing. On one hand, the repressive nucleosome nuc-1, located immediately downstream of the transcription start site, is maintained hypoacetylated by histone deacetylases (HDACs) in latent conditions. The laboratory of the inventors have previously reported that treatment of latently HIV-1-infected cell lines with HDAC inhibitors (HDACIs) induces viral transcription and remodeling of nuc-1. In addition, histone H3 lysine 9 (H3K9) methylation was shown by the laboratory of the inventors in microglial cells and by other in T cells or patient's cells to play a major role in chromatin-mediated repression of HIV-1 expression. The histone methyltransferases (HMTs) Suv39H1, which is primarily involved in H3K9 trimethylation (H3K9me3), and G9a, which is responsible for H3K9 dimethylation (H3K9me2), have been demonstrated to play a role in HIV-1 transcriptional silencing. On the other hand, the laboratory of the inventors and others have reported that DNA methylation is another epigenetic modification involved in HIV-1 postintegration latency. DNA methylation, probably together with repressive histone modifications, contributes to “lock” the silent state of the provirus and makes its return to an active state difficult. These observations suggest that HDAC or HMT or DNA methylation inhibitors together with efficient cART constitute good anti-latency drug candidates aimed at reducing/eliminating the pool of latent reservoirs to a level bearable by the host immune system.
In this context, several clinical studies have tested the reactivation potential of an HDACI alone (Valproic acid (VPA) or Vorinostat (suberoylanilide hydroxamic acid, SAHA), two FDA-approved drugs)) in ex-vivo cell cultures isolated from HIV+ patients blood. Whereas their published results or their unpublished preliminary results are encouraging, they question the efficiency of these drugs used alone to reduce the size of the latent HIV-1 reservoirs. The laboratory of the inventors have previously shown that the combined use of two drugs (an HDACI plus a NF-KappaB inducer, prostratin) causes a synergistic reactivation of HIV-1 production i.e. a higher reactivation than the sum of the reactivations produced by each drug individually in latently-infected used cell lines. Moreover, the same drug combination reactivates HIV-1 expression in CD8+-depleted PBMCs cultures from cART-treated patients in a higher proportion of cells than observed with the drugs used alone. They have therefore demonstrated a proof-of-concept for the coadministration of two different types of therapeutically promising HIV-1 inducers together with efficient cART as a therapeutic perspective to decrease the pool of latent HIV-1 reservoirs. However, in 40% of their cultures, they could not detect any viral outgrowth following treatment with prostratin and HDACIs individually or in combination. This could result from a stronger epigenetic repression of some integrated proviruses in resting cells that would hinder an efficient viral transcriptional reactivation and expression, thereby highlighting the importance of finding new combinatory reactivation strategies. Consequently, the present invention uses the HIV-1 reactivation potential of two other classes of compounds, i.e. DNA methylation inhibitors and histone methyltransferase inhibitors (HMTIs), alone or in combination with other classes of HIV-1 inducers.